[Bug 94940] Re: mdns listed in nsswitch.conf causes excessive time for dns lookups

[Mark Thornton]

A default installation of Microsoft Small Business Server Essentials
2011 will use a .local domain. It is quite tedious to override this
choice (http://titlerequired.com/2011/08/02/installing-sbs-essentials-
using-an-answer-file/). Anyone using Ubuntu on such a network has to
remove the default mDNS entries from the nsswitch.conf file. Not
helpful.

Note that SBS 2011 is a current product, so we can expect there to be
many mycompany.local domains in use.

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Title:
  mdns listed in nsswitch.conf causes excessive time  for dns lookups

Status in “avahi” package in Ubuntu:
  Confirmed
Status in “nss-mdns” package in Ubuntu:
  Confirmed
Status in “nss-mdns” package in Debian:
  New

Bug description:
  Binary package hint: avahi-daemon

  I encountered this problem on a machine that is integrated into our
  work network. I performed a dist-upgrade to Feisty on my desktop and
  all went well. I've noticed recently that any dns based work seemed to
  take a significantly longer time then normal.

  My system is getting dns information on our company internal systems
  from two dns servers. Previously, if I tried to establish an ssh
  connection with another system I could generally expect the connection
  in under 3 secs.

  After the dist-upgrade the time went from under 3 seconds to
  approximately 25 seconds. After searching around the system I found an
  entry in /etc/nsswitch.conf that cause me a little concern. The line
  in question is:

     hosts:          files mdns4_minimal [NOTFOUND=return] dns mdns4

  I looked around a bit and it seems that the references to mdns are
  really talking about communication with the Avahi mDNS/DNS-SD daemon.
  Since this looks to be a part of a zeroconf configuration I wasn't
  expecting too much in my current environment, as we really only have
  three Mac's.

  What concerned me is the idea that if we hit files with no answer
  there is a delay while we hit the other options until we hit dns,
  which is where the information I seek existed.

  For an experiment I tried two separate tests. The first changed the
  line to looks like:

      hosts:          files dns mdns4_minimal [NOTFOUND=return] mdns

  The change should have improved the time, but I was still looking at
  approximately 23 seconds to return a command prompt on the destination
  machine.

  Finally, I change the entry to simply:

      hosts:          files dns

  After this change I was again receiving the destination command prompt
  in under 3 seconds. I don't know if simply changing the file will
  correct the problem long-term or not. Seems to help me, but might be
  the way to go for most Ubuntu users.

  ProblemType: Bug
  Architecture: i386
  Date: Thu Mar 22 18:10:54 2007
  DistroRelease: Ubuntu 7.04
  Uname: Linux samdesk 2.6.20-12-generic #2 SMP Wed Mar 21 20:55:46 UTC 2007 i686 GNU/Linux

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